This invention relates to broadband amplifiers which use feed-forward techniques to reduce distortion. According to well-known feed-forward principles, a sample of an amplifier's output signal is compared with a sample of its input signal. The difference, which is proportional to the error introduced by the amplifier, is amplified and subtracted from the output signal to thereby reduce distortion. The feed-forward technique therefore requires signal splitting at the input and output of the main amplifier and signal combining at the input and output of the error amplifier. Because of the frequencies involved in broadband transmission, the coupling devices used for the signal splitting and combining must maintain matched impedances as well as a specific power dividing ratio. In addition, in order to prevent amplifier instability, due to regenerative feedback, they must be directional in nature. Broadband directional couplers with specific impedance matching however, are difficult to design, and therefore expensive.
An object of this invention is a broadband feed-forward amplifier which does not require specific couplers.
A second object is a broadband feed-forward amplifier which uses feedback amplifier elements to allow impedance matching with simple resistive coupling networks.